This invention is in the field of medical machines for sequentially emptying and refilling bags of fluid for peritoneal dialysis. Recently, there has been a resurgence of interest in the nephrology community in peritoneal dialysis. This method of treatment of kidney treatment is somewhat slower than hemodialysis since it utilizes the diffusive properties of the peritoneal membrane (the shiny, thin membrane which covers all of the abdominal cavity contents) for transfer of body waste. The peritoneum is utilized as an effective excretory organ by placing a sterile balanced-salt solution into the abdominal cavity and leaving the solution therein for a certain period or dwell time. During the dwell time, waste molecules from the blood diffuse across the peritoneal membrane into the clear salt solution.
The relatively slow nature of peritoneal dialysis as compared to hemodialysis or the extracorporeal purification of blood may be offset by schedules of dialysis allowing for continuous treatment of the patient. In 1975, Popovich and Moncrief described an exchange method for peritoneal dialysis in which two liters of fluid are placed in the patient's abdomen and left for a period of four to eight hours. Subsequently, the fluid was drained and two liters of new fluid was placed into the abdomen. A modification of this procedure by Oreopoulos, in 1977, included use of peritoneal solution in two liter bags. The bags could then be rolled up and carried by the patient in the empty state during the dwell time. These patients were ambulatory and required only one bag connection for both infusion and drainage of fluid. This method of dialysis has expanded widely, with over 5,000 patients in the United States now receiving such dialysis. The method is from a chemical standpoint the most effective method of treatment of renal failure by dialysis. It is known as "Continuous Ambulatory Peritoneal Dialysis", (CAPD) used in ambulatory outpatients. In a hospital setting, for patients who are in an intensive care unit or ward situation, the method is known as "Continuous Equilibrium Peritoneal Dialysis", (CEPD).
The significant limitation of this novel procedure has been the development of peritonitis by the patients, in which peritonitis is mostly induced by chance contamination of the spike during insertion and removal from the tubular outlet of the bag of fluid. To avoid the infection, meticulous care must be taken by the patient or hospital staff during the spike exchange period. The usual spike exchange and drainage procedure takes approximately 1/2 hour resulting in 2 to 3 hours of manpower input per day. Such a procedure in a hospital setting is not only very costly but in many cases ineffective in avoiding infection.
An alternate mechanized method of such peritoneal fluid cycling has been proposed by Diaz-Buxo wherein a machine performs the cycling of peritoneal fluid during the nighttime hours and allows the patient to be ambulatory with a two liter residual peritoneal fluid in the abdomen during daytime hours. Use of a machine compresses the time necessary for performance of continuous peritoneal dialysis to two segments, one setting of the machine and one in taking the machine down and sealing off the abdominal cavity tubing. Several types of machines have been developed. The R-O machine is a mechanical proportioning machine producing sterile water and mixing it in a 1-20 dilution with concentrate. The American Medical Products Machine is a gravity powered machine utilizing 4 to 8 bags or bottles of fluid suspended above the bed of the patient. A large drainage bag of 4 to 12 liters attached to the same tubing set is required and is suspended below the bed of the patient.
All of the machines to accomplish the perintoneal dialysis have certain disadvantages. Some of the machines are somewhat complicated requiring resterilization after each use and utilizing electrical or mechanical scales for determining outflow volumes. A significant number of "alarms" may be expected during each operation. Some machines require a rather large and long tubing set which must be connected to the bottle suspended at a meter above the bed and with a drainage bag below the bed. In addition, a "warming bag" is utilized for warming fluid before the fluid enters the abdomen of the patient. The outflow volume must be electro-mechanically determined by a sensitive weighing mechanism which must weigh up to the total of 12 liters outflow volume. Some of the machines are rather bulky weighing over 40 lbs without fluid and standing over six feet tall when assembled. In certain cases, the bag connections must be made with the same type of manual clamps utilized for CAPD in the home since there is no firm fixation of the "nipple" or spike inlet of the bag when placed on the machine. Instead, the bags are merely hung vertically at the top of the machine and the critical entrance to the bag is a freely movable somewhat floppy position.
It would be ideal to have a cycler machine which utilizes a short tubing set just large enough to span the physical distance needed to separate the bags. For example, each bag need be separated only by about 4 inches when full. In order to achieve a short tubing section, it is necessary to have a physical method of compression of each bag or expansion of each bag and to rely on this force to fill and empty the bag rather than to utilize the position of each bag alone (above and below the abdomen) for generation of hydrostatic pressure. Such compression and drainage of each bag would necessarily require considerable amount of force if done by a piston or air pressure cycler. On the other hand, a considerable amount of force is present in the weight of the bag alone with six 2-liter bags weighing approximately 12 kilograms. By utilizing the weight of the entire fluid for compression of each bag, then the energy input to each bag would be six times that obtained from the weight of one bag's fluid alone. Heretofore, the potential energy of each 2-liter volume of fluid of a standard cycler is wasted once the fluid has drained into the drainage bag. The weight of fluid in such a gravity powered cycler could be utilized to augment infusion of further bags of fluid. By supporting the bag at a certain distance approximately 2 feet from the floor of the room, further energy may be gained from the bags as they inch their way towards the floor. Such a two foot elevation of the dialysis fluid still allows adequate drainage of the abdomen since there is significant intraperitoneal pressure of 10 to 20 cm of water, with the patient elevated approximately two to three feet off the floor by his bed or chair. Disclosed herein is such a machine which utilizes a short tubing set, avoids the necessity of heating of the drainage bag and returns the fluid to the same bag from which it is delivered. The cycler is gravity powered, utilizing energy obtained from the weight of bags which have already been drained, as well as those which are yet to be used in the abdomen. The cycler is therefore a Short-Tubing Set Gravity Powered Peritoneal Cycler or STS-GPC.